Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $81.71   13.255%   $92.5407   $92.54   $92.55   $92.50  
  Purchase #2 $98.84   3.865%   $102.6602   $102.66   $102.65   $102.70  
  Purchase #3 $14.28   8.592%   $15.5069   $15.51   $15.50   $15.50  
  Purchase #4 $186.66   8.782%   $203.0525   $203.05   $203.05   $203.10  
  Purchase #5 $183.44   6.776%   $195.8699   $195.87   $195.85   $195.90  
  Purchase #6 $213.53   11.113%   $237.2596   $237.26   $237.25   $237.30  
  Purchase #7 $173.84   5.565%   $183.5142   $183.51   $183.50   $183.50  
  7 purchase totals = $952.30       $1,030.4040   $1,030.40   $1,030.35   $1,030.50